Java for LeetCode 085 Maximal Rectangle

Given a 2D binary matrix filled with 0's and 1's, find the largest rectangle containing all ones and return its area.

解题思路：

求01矩阵中，全是1的子矩阵的最大面积。

把矩阵按照每一行看做是直方图，可以转化为上一题，JAVA实现如下：

	static public int maximalRectangle(char[][] matrix) {
		if(matrix.length==0||matrix[0].length==0)
			return 0;
		int result=0;
		int[] dp=new int[matrix[0].length];
		for(int i=0;i<matrix.length;i++){
			for(int j=0;j<matrix[0].length;j++)
				if(matrix[i][j]=='1')
					dp[j]++;
				else dp[j]=0;
			result=Math.max(result, largestRectangleArea(dp));
		}
		return result;
	}
	 public static int largestRectangleArea(int[] height) {
	        Stack<Integer> stk = new Stack<Integer>();
	        int ret = 0;
	        for (int i = 0; i <= height.length; i++) {
	            int h=0;
	            if(i<height.length)
	                h=height[i];
	            if (stk.isEmpty() || h >= height[stk.peek()])
	                stk.push(i);
	            else {
	                int top = stk.pop();
	                ret = Math.max(ret, height[top] * (stk.empty() ? i : i - stk.peek() - 1));
	                i--; 
	            }
	        }
	        return ret;
	}